Field of the Invention
The present invention relates to a drive control apparatus configured to control the driving of a movable member, and more particularly, to a lens apparatus and an image pickup system that include a drive control apparatus configured to control the driving of a movable optical member.
Description of the Related Art
Lens apparatus in which a movable optical member driven by a motor is controlled have employed feedback control to reduce to zero a difference between a control target and the position of the movable optical member, which is detected by a position detector. An example thereof is disclosed in Japanese Patent Application Laid-Open No. 2005-323488.
When a drive transmission mechanism configured to transmit a driving force from the motor to the position detector is, for example, a gear train in the technology of Japanese Patent Application Laid-Open No. 2005-323488, play (clearance, e.g., backlash) between gears of the gear train causes a difference between the driving position of the motor, which is a control target, and the result of position detection by the position detector, and a phase inversion of a control output and the position detection result due to the difference may lead to oscillation phenomena.
The oscillation phenomena are brought about especially when the movable optical member moves under the influence of an external force, e.g., gravity, thereby causing the detected position of the driven member to change (forward with respect to the direction of driving) within the extent of play irrespective of the motor's driving.